Black-clawed Coral Crab

Geographical Origin and Habitat: Widely distributed throughout the tropical Indo-Pacific, from East Africa and the Red Sea to Hawaii and Polynesia. Found exclusively within live branching colonies of Acropora corals.

Taxonomy: Member of the family Xanthidae. A tiny crab species measuring about 1.5-2 cm in width. The carapace is typically bumpy or granular, with short legs covered in spiny hairs. Grows to 1.8 cm.

Social Behavior: Commensal symbiont. Lives protected between the branches of Acropora. It may defend its host from small intruders, but can exhibit parasitic feeding behavior if the host colony is small.

Coloration and Sexual Dimorphism: Body and legs are pale green, greenish-grey, or light cream. The dactyli (tips of the claws) are a contrasting glossy deep black or dark brown. Eyes are orange. No visible sexual dimorphism.

Tank Setup: Must be housed in a mature reef aquarium of 12-15 gallons or larger with live, healthy branching Acropora corals. Does not require empty shells.

Diet and Feeding: Feeds on coral mucus, microalgae, and occasionally host coral polyps. In aquariums, it also catches suspended food like fine mysis or powdered foods from the water column.

Water Quality: Reef parameters. Salinity SG 1.021-1.025, pH 8.1-8.4, temperature 22-28°C. Highly sensitive to copper treatments, elevated nitrates, and sudden salinity drops.

Compatibility and Tankmates: Generally compatible with mature SPS reefs. May slightly damage small Acropora frags by feeding on polyp tissue. Compatible with peaceful small fish.

Aquarium Breeding: Microscopic larval stages are pelagic and complex, and do not survive standard home aquarium filtration systems.

Risks and Diseases: Direct dependence on the host coral; if the coral host dies, the crab will experience high stress and likely perish. Requires stable calcium and iodine for molting.